The present invention relates to circuits and methods for generating negative voltages in an integrated circuit, and more particularly, circuits and methods for implementing stable load-independent negative voltage regulators.
The performance increases of new integrated circuits (IC), and particularly Programmable Logic Devices (PLD), including Field-Programmable Gate Arrays (FPGA), can result in significant increases in power consumption, introducing the risk of devices that consume unacceptable amounts of power. Power consumption becomes a critical issue because static power can increase dramatically with higher component densities. Static power consumption rises largely because of increases in leakage current, including tunneling current across the thinner gate oxides that are used in new processes, as well as subthreshold leakage (channel- and drain-to-source current). Also, without any specific power optimization effort, dynamic power consumption can increase due to the higher density of switching transistors combined with the higher switching frequencies that are attainable.
Although power requirements vary across different applications, the benefits of lower power consumption are applicable to any hardware platform because of the inherent cost, complexity, and reliability advantages. Today's design trends—such as increasing compactness of system form factors and portability—have significantly heightened the sensitivity to power consumption in PLDs, in particular. In “tethered” applications where wall power is the primary source, system enclosures are becoming dramatically thinner and smaller, restricting airflow, heat sink, size, and other thermal management solutions. In portable applications, a relatively new domain for FPGAs, battery-life objectives place new restrictions on both static and dynamic power consumption. These shifts in design goals make power consumption one of the critical factors when choosing and programming ICs.
As a result, there is a need to manage the balance between power and performance in today's ICs. One of the ways to accomplish lower power consumption is by using negative voltages to body bias transistors, which requires stable current-load-independent negative voltage regulators with variable output. The current load for the negative voltage regulators can vary within a very large range.
In addition, because of process variations, there can be silicon where the substrate leakage is very low, or silicon where the substrate leakage is very high. This presents problems for the circuit designer, because circuits must operate under a wide range of current loads. As a result, negative voltage regulators operate under a wide range of current loads, and the outputs of the negative voltage regulators have to be stable and independent on whether the current load is small or large. More specifically, the loop gain must be independent of the load current.
It is in this context that embodiments of the invention arise.